Instructions for building and booting Linux: Difference between revisions

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[http://wiki.linux-xtensa.org/index.php/Buildroot_Snapshots snapshot releases].
[http://wiki.linux-xtensa.org/index.php/Buildroot_Snapshots snapshot releases].


=== Download buildroot sources ===
For most users, just execute the following:
 
Buildroot is used to build the toolchain and root filesystem.
First setup a work area:


   $ cd <workdir>
   $ cd <workdir>
  $ git clone git://git.linux-xtensa.org/git/buildroot/buildroot-xtensa buildroot
  $ git clone git://git.linux-xtensa.org/git/kernel/xtensa-2.6.24 linux


where <tt><workdir></tt> is the path to an empty directory on a disk with
where <tt><workdir></tt> is the path to an empty directory on a disk with
at least 4 GB available space.
at least 4 GB available space. You end up with the following file structure,
The following creates and populates the <tt><workdir>/buildroot</tt> directory:
which is assumed by the rest of this document:
 
  $ git clone git://git.linux-xtensa.org/buildroot/buildroot-xtensa buildroot
 
=== Download Linux kernel sources ===
 
First you need to decide which kernel tree to work with.
(You can also download multiple kernel source trees of course.)
 
For now this is simple, there is just one active tree.
At the time of writing, the <tt>xtensa-2.6.24</tt> tree is the active tree.
 
The <tt>xtensa-2.6.24</tt> tree is based on the released 2.6.24 kernel
from <tt>kernel.org</tt>.
 
To get the <tt>xtensa-2.6.24</tt> tree into directory ''<dir>'' (which must not already exist),
do this:
 
  $ cd <workdir>
  $ git clone git://git.linux-xtensa.org/kernel/xtensa-2.6.24 <dir>


This creates and populates the ''<workdir>/<dir>'' directory.  If ''<dir>'' is omitted, it defaults to <tt>xtensa-2.6.24</tt> (the last non-extension part of the cloned path).  For the purposes of this document, we assume ''<dir>'' is named <tt>linux</tt>, like this:
  <workdir>/
            /buildroot
            /linux


  $ git clone git://git.linux-xtensa.org/kernel/xtensa-2.6.24 linux
If you happen to have write access to either repository, or want more details,
see the [[Repository_Access| repository access]] page.


== Install any required processor specific overlay ==
== Install any required processor specific overlay ==

Revision as of 23:35, 11 July 2008

These instructions explain how to build a toolchain, root filesystem and kernel for Linux running on an Xtensa processor. These instructions apply specifically to the XTAV60 (LX60) board.

Some general notes on these instructions:

  • They are a work in progress. If you are using the latest development sources, the build process may change, so you should be sure to get the latest version of this document at http://wiki.linux-xtensa.org/index.php/Buildroot_Build_Instructions. If you are using one of the development snapshot releases, you should use the version of the build instructions included with that snapshot.
  • The following was tested on x86 machines running RedHat Enterprise Linux 4 (RHEL4) and Fedora Core 3 (FC3). It is expected to work on newer Fedora releases (e.g., was tested on FC6) but to maintain host compatibility with Xtensa Tools, it is best to avoid Fedora releases beyond FC5. Other host distributions likely work but have not been tested.
    • NOTE: this assumes the default selection of packages in buildroot. Selecting extra packages may require a more recent host OS or more recent version of certain tools. For example, the default version of find on RHEL4 is too old to allow building all X11 packages in buildroot, so it is necessary to upgrade the host version of findutils on RHEL4 to build these packages.
  • Lines prefixed with "sudo" need to be executed as root. The rest is best executed as a non-root user. (It is possible to install git as a non-root user if root access is an issue. How to do this isn't shown here.)
  • Lines that set environment variables assume a Bourne compatible shell (e.g., /bin/sh or bash), but are easily adapted to other shells.
  • Instructions are assumed executed all in order (e.g., commands assume current directory and environment variables set earlier).


Setup your host system

If you are using one of the snapshot releases, you can skip this step.

If you want to work with the latest development sources, you will need git installed on your system.

Download buildroot and the Linux kernel

The following section describes how to download the latest versions of buildroot and of the Linux kernel. Skip this step if you are using one of the snapshot releases.

For most users, just execute the following:

  $ cd <workdir>
  $ git clone git://git.linux-xtensa.org/git/buildroot/buildroot-xtensa buildroot
  $ git clone git://git.linux-xtensa.org/git/kernel/xtensa-2.6.24 linux

where <workdir> is the path to an empty directory on a disk with at least 4 GB available space. You end up with the following file structure, which is assumed by the rest of this document:

  <workdir>/
           /buildroot
           /linux

If you happen to have write access to either repository, or want more details, see the repository access page.

Install any required processor specific overlay

This step is required if you are targeting a custom Xtensa processor. If you use a Diamond 232L Standard Core, you can skip this step.

To configure buildroot and the kernel to use a custom Xtensa processor configuration, you need to overlay a set of files customized for your processor configuration onto toolchain sources (gcc, binutils, gdb, etc) and the Linux kernel. This process has been automated using a script located in the buildroot source tree. For usage information, you can invoke it without arguments:

  $ cd <workdir>
  $ ./buildroot/target/xtensa/xt-buildroot-overlay-install

which displays a help message similar to the following:

xt-buildroot-overlay-install version 1.3
Usage:  xt-buildroot-overlay-install <parameters> [<options>]
Where <parameters> are:
  -t file.tgz     Specify path to the Xtensa Linux overlay tarball, typically
                  <xtensa_root>/src/xtensa-config-overlay.tar.gz
  -b dir          Path to the base of the buildroot source tree, in which
                  package specific overlay tarballs get installed.
  -k dir          Path to the base of the Linux kernel source tree, in which
                  the Linux kernel specific overlay gets installed.
  -c config_name  Name for the Xtensa processor configuration as it will be
                  known to the open source community.  Must be a lowercase
                  identifier, starting with a letter, consisting of letters
                  and numbers and underscores, not ending with underscore
                  and not containing consecutive underscores.  For examples:
                     dc232b , dc232b_be , mmubasele , fsf , s5000 .
  -l long_name    Long name for the Xtensa processor configuration, human-
                  readable with spaces etc allowed (must be quoted).
                  For example:  'Diamond 232L Standard Core Rev.B (LE)'
                  Try to keep it within approximately 40 characters.
And <options> are:
  -f              If package specific overlay tarballs already exist in
                  the destination source tree, overwrite them without asking.
  --help          Show this usage message.

Note that the Xtensa Linux overlay tarball MUST be obtained from an Xtensa core package built using release RB-2008.3 or later.

Here is an example invocation of the overlay installation script:

  $ ./buildroot/target/xtensa/xt-buildroot-overlay-install -t blinkcore-config-overlay.tar.gz \
        -b ./buildroot -k ./linux -c superzip -l "ChipCorp SuperZIP Blink Accelerator Core"

The script extracts some relevant information from the overlay tarball, presents it along with relevant parameters to the user, and prompts for confirmation before proceeding.

The chosen processor name (-c option) must be unique among known Xtensa processors. It is also probably wise to avoid names confusingly similar to other (non-Xtensa) processors. If you expect at some point to contribute support for your custom processor to the open-source community, this name will likely be long-lived. (One way to contribute support for a custom processor might be to submit the overlay tarball or files to the linux-xtensa.org maintainers.)

In the steps below, buildroot and the Linux kernel must be configured (in their respective make menuconfig steps) to select the custom Xtensa processor option. This presents an extra configuration menu entry where you must provide the name of the Xtensa processor. Set it to the same name as was specified in the -c option above.

Build a toolchain and root filesystem using buildroot

Note: for more details on generic buildroot topics not covered in this simple how-to, see buildroot.uclibc.org.

Configure buildroot

The first time you configure buildroot, start with defaults for your Xtensa processor:

  $ cd <workdir>/buildroot
  $ ./target/xtensa/setup-config <corename>

where <corename> is the overlay name of your selected Xtensa or Diamond core (e.g., dc232b). If you omit <corename>, a help message and a list of currently installed Tensilica core overlays is displayed.

Optionally, you can then customize your buildroot configuration, such as selecting additional packages, setting various parameters, and so on. The following make targets provide a curses (text-based graphical) interface for configuring buildroot, the uClibc C library, and busybox, respectively. (Note: You need the TERM environment variable properly set for these curses based tools to work.)

  $ make menuconfig
  $ make uclibc-menuconfig
  $ make busybox-menuconfig

Build buildroot

Just type:

  $ make

THIS WILL TAKE A LONG TIME (from about 30 minutes with defaults on a 3 GHz Pentium 4, to perhaps an hour or many depending on your system and on whether you enabled extra packages in your buildroot configuration).

Wait patiently for the build to complete. This builds an entire toolchain as well as some basic packages, and constructs a root filesystem. It might build many more packages if you selected them earlier with menuconfig.

If Something Goes Wrong

Perhaps you missed some step above and the build fails. Or you're just switching to a different processor configuration, or making some change with unknown dependencies. Either way, you'll probably need to fix the error and/or make the change, and redo the whole build. The above make command usually works fine if you just added a package using menuconfig, but otherwise does not check many dependencies, so it will usually NOT rebuild things that depend on whatever you have fixed or changed. Here's one way to retry the make from scratch without having to wipe out the buildroot directory tree completely and start again from the git cloning.

 $ rm -rf *build_xtensa* binaries
 $ make

It is not necessary to empty the 'dl' subdirectory, which contains tarballs downloaded from the Internet, nor the .config file, which contains the buildroot configuration. Customizations to the uClibc and busybox configurations should have ended up getting saved in target/xtensa/uClibc.config and target/xtensa/busybox-config, respectively, so hopefully are preserved by the above sequence.

Build and Run a Linux Kernel on the XTAV60 or XTAV200 Board

References to the XTAV60 board refer to the combination of the Avnet LX60 (Xilinx) Development Board and a Tensilica-provided FPGA bitstream containing a configured Tensilica processor and basic peripheral IP. For more details, please refer to the Tensilica Avnet LX60 (XT-AV60) Board User's Guide.

Similarly, references to the XTAV200 board refers the combination of the Avnet LX200 (Xilinx) Development Board and a Tensilica-provided FPGA bitstream containing a configured Tensilica processor and basic peripheral IP. For more details, please refer to the Tensilica Avnet LX200 (XT-AV200) Board User's Guide.


Configure the kernel

The kernel build is a two-step process: configure the kernel, and build it. First, before we can do anything with the kernel, set your PATH to point to the toolchain built using buildroot.

  $ export PATH="<workdir>/buildroot/build_xtensa_<cname>/staging_dir/usr/bin:$PATH"

where <cname> is the name of the Xtensa processor configuration you selected when building the toolchain (e.g., dc232b).

Now setup a destination for kernel builds. We usually like to have the build directory separate from the source directory, so we use 'O=</destination/path>' in kernel make commands. If you'll be routinely building multiple configurations of the Linux kernel, it's good to have some naming conventions for the build directory. For example, to experiment with multiple target platforms but only one processor configuration, we include just the platform name here:

  $ mkdir build-xtav60

Let's start with the default kernel configuration for the Avnet board (which works on both XTAV60 (LX60) and XTAV200 (LX200) boards) as follows:

  $ cd linux
  $ make O=../build-xtav60 ARCH=xtensa KBUILD_DEFCONFIG=lx60_defconfig defconfig

This configures the kernel using the default configuration found in arch/xtensa/configs/lx60_defconfig.

NOTE: This kernel configuration has nothing to do with Xtensa processor configuration. That comes next.

Let's now customize this a little bit to select the correct Xtensa processor configuration, and to bundle the root filesystem into the kernel:

  $ make O=../build-xtav60 ARCH=xtensa menuconfig

Under General setup, make sure the Initial RAM filesystem and RAM disk (initramfs/initrd) support entry is enabled. Underneath that, edit Initramfs source file(s), and enter the path to the cpio formatted root filesystem generated by buildroot:

     <workdir>/buildroot/binaries/uclibc/rootfs.xtensa_<cname>.cpio.gz

(Don't forget to replace <workdir> with the appropriate full path and <cname> with your Xtensa processor configuration name.)

Under Processor type and features, make sure the Xtensa Processor Configuration is correct and matches the processor configuration name you used to build the toolchain with buildroot (for example, dc232b for Diamond 232L Rev.B). The kernel build selects a toolchain and processor variant specific headers based on this selection. If the desired processor configuration does not appear explicitly in the list, simply select Custom Xtensa processor configuration and enter the processor configuration name (all lowercase) into the next menu parameter, Xtensa Processor Custom Variant Name.

Back in the main menu, under Platform options, make sure the CPU clock rate entry is set correctly according to the following table:

Board Frequency selected in XPG
(MHz)
CPU clock rate setting
(kHz)
XTAV60 (LX60) 30 33333
40 40000
50 50000
XTAV200 (LX200) 30 31250
40 41667
50 50000

Exit menuconfig, saving your configuration changes.

Backup your configuration outside the build directory. For example:

  $ cp ../build-xtav60/.config config.xtav60.saved

If you do a clean rebuild of the kernel (e.g., "rm -rf ../build-xtav60") you can now configure it with simply:

  $ mkdir ../build-xtav60 ; cp config.xtav60.saved ../build-xtav60/.config

Of course if you update the kernel, you'll probably again have to do:

  $ make O=../build-xtav60 ARCH=xtensa  menuconfig

and save a new copy of your configuration.

Build the kernel

  $ make O=../build-xtav60 ARCH=xtensa

The build will issue a few warnings which are normal. Once complete, the bootable image is in:

     <workdir>/build-xtav60/arch/xtensa/boot/Image.elf

and the uncompressed ELF file containing kernel symbols is in:

     <workdir>/build-xtav60/vmlinux

There is also a RedBoot bootable image (if you use RedBoot) in:

     <workdir>/build-xtav60/arch/xtensa/boot/zImage.redboot

Install Xtensa Tools for the selected core

If you opt to download the kernel over OCD, you need xt-gdb which is part of Tensilica's Xtensa Tools package. This must be obtained from Tensilica, and is not the same toolchain as built by buildroot. You also need to install the corresponding Tensilica core package, so that the Xtensa Tools know about your particular configured Tensilica core.

The toolchain built using buildroot can be configured to include GDB, but that version of GDB does not support communicating with Tensilica's Xtensa OCD Daemon, and thus cannot be used to download the kernel over OCD.

In this example, it is assumed that the machine hosting the Xtensa Tools has access to the <workdir> directory tree.

Install and setup the Xtensa OCD Daemon

Setup and connect your JTAG probe, etc.

Connect a terminal server

At 38400 bps 8N1 no flow control to the XTAV60 serial port.

Optionally, setup networking

This step is optional.

Setup the board's MAC address using dipswitches (see XTAV60 or XTAV200 board docs as appropriate) and connect the board to a network that has a DHCP server that will respond to that MAC address. If you don't do this step, you'll simply not have network access, and the boot process will take a minute or so longer while the kernel times out waiting for a BOOTP response. You can edit the kernel configuration and rebuild the kernel to avoid using bootp (in particular, remove "ip=bootp" from the kernel cmdline).

Download and run the kernel

Reset the board (see board documentation).

Using Xtensa Tools, invoke:

  $ xt-gdb <workdir>/build-xtav60/arch/xtensa/boot/Image.elf
  (xt-gdb) target remote <ocdhost>:20000 0
  (xt-gdb) reset
  (xt-gdb) load
  (xt-gdb) set $pc = &_ResetVector
  (xt-gdb) symbol-file <workdir>/build-xtav60/vmlinux
  (xt-gdb) c

where <ocdhost> is the IP address or DNS name of the machine running the Xtensa OCD daemon. The Linux kernel should start booting as soon as 'c' (continue) is executed.

You should eventually get a login prompt. Just login as root (no password).

Try various Linux commands. Look at /bin, /sbin, /usr/bin, etc to see what's available.

Note: no need to setup an NFS or TFTP server. The filesystem is contained within the kernel image. You may be able to mount other filesystems over NFS though, if you wish, after booting.

Build and Run a Linux Kernel on the Instruction Set Simulator (ISS)

You can build and run a Linux kernel in the Xtensa Instruction Set Simulator (ISS). The following instructions have only been tried with an ISS from the RB-2008.3 release of Xtensa Tools. Bear in mind that the XTAV60 port is likely much more stable than the ISS port of Linux at this point in time.

Note: Depending on your host OS version, you may need to install Xtensa Tools on a separate machine.

Configure and Build the Kernel for ISS

Repeat all the same instructions as above for building the kernel for the XTAV60 board, except that when initially configuring the kernel, start from the ISS platform template instead:

  $ mkdir build-iss
  $ cd linux
  $ make O=../build-iss ARCH=xtensa KBUILD_DEFCONFIG=iss_defconfig defconfig

This configures the kernel using the default configuration found in arch/xtensa/configs/iss_defconfig.

Also, when running menuconfig:

  $ make O=../build-iss ARCH=xtensa  menuconfig

in addition to setting up the initramfs filesystem, do the following. Under Bus Options, deselect PCI support. Under Platform Options, deselect Default bootloader kernel arguments.


Continue configuring and building the kernel as usual.

Run the Kernel on ISS

Using Xtensa Tools, invoke:

  $ xt-gdb <workdir>/build-iss/arch/xtensa/boot/Image.elf
  (xt-gdb) target sim --turbo
  (xt-gdb) symbol-file <workdir>/build-iss/vmlinux
  (xt-gdb) run

Wait patiently while Linux boots ... (maybe a minute)

Login as root (no password).

Note: Input via ISS is cooked, so everything typed gets echoed. Also, time as reported by the kernel does not progress according to true wall-clock time: it currently depends on a simulated processor clock, which advances at various speeds according to load.